The present invention relates to an eyeglass lens grinding apparatus for grinding the periphery of an eyeglass lens.
As disclosed in U.S. Pat. No. 5,347,762, a typical eyeglass lens grinding apparatus for grinding the eyeglass lens periphery is designed such that a lens to be processed is clamped by lens rotating shafts, and a carriage holding the lens rotating shafts are pivotably moved using a pulse motor so as to control an axis-to-axis distance between the rotating lens and an rotating abrasive wheel, thereby processing the lens while depressing the lens onto the abrasive wheel.
To prevent breakage and axial offset of the lens during processing, it is necessary to set processing pressure to an appropriate level. For this reason, the apparatus employs such a mechanism that a carriage is pressed by a spring force in the direction toward an abrasive-wheel rotating shaft during processing of the lens, and the carriage is relieved in a direction away from the abrasive wheel if the force exceeding the processing pressure adjusted by the spring force is applied to the lens.
The apparatus is further provided with a processing completion sensor for detecting whether or not the lens has been processed to a predetermined size. The apparatus controls the processing while monitoring (detecting) whether or not the relief mechanism works using this sensor.
If the apparatus having the above-described arrangement is further provided with a motor for adjusting the spring force of the relief mechanism, then it may be possible to adjust the processing pressure depending on the difference in the lens material prior to processing. However, the processing pressure is generally constant during processing. For this reason, if the processing pressure is set to a high level, an excessively high torque is applied to the lens rotating shafts in an early stage of processing where the lens diameter is large, which may results in the axial offset. If the processing pressure is set to a low level to prevent such situation, the overall processing time is long.
In addition, with apparatus having the above-described arrangement, the range in which processing has not been completed can be known by the processing completion sensor, but it has been impossible to ascertain how much such a portion remains unprocessed (unprocessed amount). For this reason, it has been impossible to change the processing conditions in correspondence with the unprocessed amount.
Further, the relief mechanism as described above is complex in construction, and is disadvantageous in terms of cost.